A reflector telescope of this kind is known as Mauna Kea reflector telescope with 10 m reflector diameter being still in the planning stage (Sterne und Weltraum, 1984/August-September, p. 412, Appl. Optics, No. 14, 2631-2641).
In this reflector telescope, the primary reflector is formed of 36 hexagonal reflector bodies forming, in a honey-comb structure, the reflector surface, in the center of which a reflector body being omitted for observation purposes in the Cassegrain focus. Manufacture of the individual hexagonal reflector bodies themselves is very problematic. They are off-axis segments of a paraboloid to be cut in hexagon shape (Appl. Optics, vol. 19(1980), No. 14, 2332-2340).
When manufacturing, as part to be fashioned, a circular part is selected to be deformed by accurately defined shearing and bending forces acting on the borders. Into the deformed blank, a spherical shape is ground. Then, the forces exerted are removed. As far as the forces have been selected properly, each reflector body accepts the desired shape of a paraboloid segment of the primary reflector after unloading. It has been found out, however, that faults occur when cutting to hexagonal shape.
Furthermore, depending on the position of the primary reflector of the reflector telescope, on thrusts due to wind and on temperature variations, the positions of the individual very thin-walled hexagonal reflector bodies have to be readjusted. For this purpose, the support points of each reflector segment are connected with three position controllers to refocus the the reflector body and to adjust it in two inclination directions. At the edges of the reflector bodies, sensors are provided measuring the displacements of adjacent reflector bodies with respect to each other. Together with three inclination sensors measuring the total curvature of the reflector body, they provide information to be processed in a computer system controlling the in total 108 position controllers. With a total 168 different sensors, redundancy is large enough that failure of individual sensors can be tolerated. In this arrangement, however, the front sides of the reflector bodies are left free from disturbing monitoring systems. Occasionally, only, a readjustment has to be performed by means of a constellation, such that even infrared observations will be possible by day. Sensors and position controllers must operate with an accuracy of at least 50 nm.
In theoretical investigations of the primary reflector of the reflector telescope described in DE patent 35 38 208, the reflector bodies of which are circular-disk shaped, such that between the individual reflector bodies, free spaces for the support of the reflector bodies and for the supporting bars structure or its shadow areas are formed, it has been found out that the free spaces put into question the infrared suitability of the primary reflector. The metal components in the area of the free spaces of the support structure of the primary reflector transmit thermal radiations to the detector arranged in the focus of the primary reflector and disturb the signal to be received from space.
Infrared suitability of the primary reflector is necessary to detect dark bodies in space, being present as weight, or mass but not visible to the human eye by means of the primary reflector. Theoretically, the phenomenon of own infrared thermal radiation of the free spaces can be excluded by technical counter-measures. They are, however, extremely expensive.
The investigations performed because of the theoretical considerations with respect to the reflector telescope according to DE patent 35 38 208, those investigations questioning the infrared suitability of this primary reflector, led to theoretical investigations of the primary reflector of the Mauna Kea reflector telescope with 10 m reflector diameter. Here, too, disturbing infrared radiations have been discovered, in spite of the basically closed reflector surface. Said infrared radiations could be guided back to the sensors arranged in the area of the contact lines of the adjacent hexagonal reflector bodies, said sensors measuring the displacement of adjacent reflector bodies with respect to each other. The primary reflector of the Mauna Kea reflector telescope has in total 168 displacement sensors, with in total 36 hexagonal reflector bodies. These, too, radiate an appreciable amount of radiation, resulting, again, in disturbing infrared radiation. Thus, the primary reflector according to the state of the art does not possesses the problem that the individual reflector bodies ground under load are only ground in the form of an aspherical off-axis section, but the lack of infrared suitability, due to the absolutely necessary displacement sensors, is also a problem. Finally, the fact that the outer contour of the primary reflector composed of hexagonal reflector bodies is not uniform has resulted in negative effects in the point image as well as in the modulation transmission function.